PURPOSE: To facilitate removal of spacer by arranging a screw in a trough having inner face adhered with yet-solidified mortal then rotating to form the surface of yet-solidified mortal.

CONSTITUTION: A screw 3 fixed with a spacer 15 is supported by upper and lower bearings 4, 5 in a trough 10 having inner face adhered with yet-solidified mortal and arranged at the position same with actual operating state then driven by a drive motor 6. Since the spacer 15 is stretched sufficiently by a fastener 14, yet-solidified mortal at further inside than the outermost rotary locus is scratched by the spacer 15 and carried out of trough 10. Consequently, a mortal casing 7 having cross-section matched with the flexture curve of screw 3 is produced. With such arrangement, production period of casing 7 is shortened to facilitate mount/dismount of spacer 15.